Dental caries is a major dental disease that affects the majority of the population. In the early part of the 20th century, investigators discovered that fluoride was effective in reducing the incidence of caries. Since that time, fluoride research has developed, and it is now well accepted that fluoride treatments benefit dental health.
Fluoride has several principal anti-cariogenic mechanisms. For example, in early dental caries, the acids formed by bacteria cause demineralization of the enamel (breakdown of the tooth structure with a loss of mineral content). Fluoride can enhance remineralization and inhibit demineralization during the earliest stages of the carious process. Fluoride from fluoridated water or fluoride toothpaste is, in part, taken up by plaque, and the majority of the fluoride provided in this manner is stored therein in bound form rather than ionic form. Subsequently, if the pH of the oral environment is lowered, bound fluoride is then released. This released fluoride then acts with calcium and phosphate ions to help reverse the effects of early demineralization.
Fluoride also acts antibacterially, in that fluoride in plaque can inhibit glycolysis (where fermentable carbohydrates are metabolized by cariogenic bacteria to produce acid). Finally, fluoride from fluoridated water or fluoride supplements, when incorporated into the developing dental enamel, can strengthen it and make it more decay-resistant. Thus, fluoride's benefits are particularly beneficial for the developing teeth of children.
Professionally administered fluorides include gel-tray applications, solutions, foams and pastes. However, over-the-counter fluoride sources such as mouthrinses, toothpastes and gels are more commonly used by consumers.
Dentifrices that are widely available typically contain fluoride ions in the range of 1,000 to 1,500 ppm. However, for some segments of the population, higher amounts of fluoride may be even more beneficial. Some patients often suffer from either more aggressive caries, or are otherwise at a higher risk of dental decay than the general population. Those patients may benefit from special dentifrices for treating high levels of caries that incorporate high levels of fluoride ions. For example, some such dentifrices incorporate sodium fluoride as a fluoride ion source, in amounts of over 1,500 ppm, 2,000 ppm or 5,000 ppm. Such compositions are highly effective in anticaries treatment.
However, a potential complication encountered with many dental applications is that of tooth sensitivity among consumers, for various health-related reasons. Treatments for sensitive teeth can vary. For example, potassium nitrate is a well-known tooth sensitivity agent used in commercial dentifrices. See, e.g., U.S. Pat. No. 3,863,006 to Hodosh. Other sensitive teeth treatments include potassium bicarbonate or potassium chloride (see U.S. Pat. Nos. 4,631,185 and 4,751,072). U.S. Pat. No. 4,990,327 lists use of strontium and fluoride ions for a sensitive teeth treatment. All patents mentioned herein are incorporated by reference in their entirety.
It would be desirable to treat sensitivity in teeth as well as caries and provide high levels of fluoride treatment, all using a single formulation. However, while teeth sensitivity agents as noted above can be effective if they are added in requisite effective treatment amounts, it is difficult to maintain the effective properties of the fluoride in an oral care composition that also includes such a sensitivity agent. This is because the fluoride (F−) ions tend to precipitate out when effective amounts of potassium nitrate are added. This is due to the inherently low solubility of fluoride ion sources such as sodium fluoride (usually less than 5%). On the other hand, if more solvent is added, the composition changes and tends to lose the desirable physical characteristics associated with an acceptable over-the-counter or prescription dentifrice having both such components.
Thus, there is a need in the art for a high-fluoride content oral care composition that is also capable of treating sensitive teeth, that is available in a single, easy-to use oral care composition, such as a dentifrice and more particularly a toothpaste, and that allows for the successful dissolution of both the high levels of fluoride required and the sensitivity agent. This would be beneficial for those patients who need high levels of fluoride and also suffer from sensitive teeth. It is further desirable to develop such a composition in which the anticaries activity of the fluoride ion is maintained successfully over time.